#include <stdio.h>
#include <stdlib.h>

int main (int argc, char const* argv[])
{
    int e, ans, i;

    while (scanf("%d", &e) != EOF) {
        ans = 0;
        for (i = 1; i <= e; i++) {
            ans += i;
        }
        printf("%d\n", ans);
        printf("\n");
    }

    return 0;
}
